1. Field of the Invention
The invention relates to an engine, more particularly to a rocker arm for an engine.
2. Description of the Related Art
Referring to FIG. 1, a conventional rocker arm 1, such as that disclosed in U.S. Pat. No. 5,038,726, is formed as a one-piece metal plate, is pivotally supported by a supporting frame, and has one end portion 12 driven by a push rod, another end portion 13 engaging a valve stem, and an intermediate portion 11 formed with an opening 111 of generally trapezoidal configuration defined by a lower edge 116 longer than a round upper edge 115, and two straight lateral edges 114 interconnecting the upper and lower edges 115, 116. The lower edge 116 has two rounded bottom edge portions 113, and a middle portion disposed between the bottom edge portions 113 and formed with upwardly-facing pivot ball socket 112.
During operation, the conventional rocker arm 1 is pivotable between the push rod and the valve stem about a pivot ball received in the pivot ball socket 112 as a fulcrum so as to transmit power. However, due to the presence of the bottom edge portions 113, stress acting on the conventional rocker arm 1 during operation easily concentrates on a wall defining the bottom edge portions 113 and the corners between the lateral edges 114 and the bottom edge portions 113. As such, the conventional rocker arm 1 easily cracks at the bottom edge portions 113 and the corners between the lateral edges 114 and the bottom edge portions 113 after a period of use.